Illuminating lens, lighting device, surface light source, and liquid-crystal display apparatus

ABSTRACT

An illuminating lens includes a light entrance surface, a light exit surface, and a reversing surface. The light exit surface has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on the optical axis, and the second light exit surface extends outwardly from the periphery of the first light exit surface. The first light exit surface includes a transmissive region in the center thereof and a total reflection region on the peripheral side thereof. The reversing surface has a shape such that the light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the reversing surface is guided to the first light exit surface by total reflection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illuminating lens for widening a range of transmission directions for light from a light source such as a light emitting diode, and to a lighting device using this illuminating lens. The present invention further relates to a surface light source including a plurality of lighting devices, and to a liquid-crystal display apparatus in which this surface light source is disposed behind a liquid-crystal panel to serve as a backlight.

2. Description of Related Art

In a conventional backlight of a large-sized liquid-crystal display apparatus, a number of cold cathode tubes are disposed immediately below a liquid-crystal panel, and these cold cathode tubes are used with other members such as a diffusing plate and a reflecting plate. In recent years, light emitting diodes have been used as light sources for backlights. Light emitting diodes have increased their efficiency recently, and are expected to serve as low-power light sources to replace fluorescent lamps. In the case where light emitting diodes are used as a light source in a liquid-crystal display apparatus, the power consumption of the apparatus can be reduced by controlling the light and dark states of the light emitting diodes according to an image to be displayed.

In a backlight of a liquid-crystal display apparatus using light emitting diodes as a light source, a large number of light emitting diodes are disposed therein instead of cold cathode tubes. The use of a large number of light emitting diodes allows the entire surface of the backlight to have uniform brightness, but the need for such a large number of light emitting diodes is an obstacle to cost reduction. In view of this, attempts to increase the output power of each light emitting diode to reduce the required number of light emitting diodes have been made. For example, Japanese Patent No. 3875247 has proposed a lens that is designed to provide a uniform surface light source with a reduced number of light emitting diodes.

In order to obtain a uniform surface light source with a reduced number of light emitting diodes, the area to be irradiated with the light emitted from each light emitting diode needs to be increased. That is, light emitted from each light emitting diode needs to be spread to obtain a wider range of transmission directions for light from the diode. For this purpose, in Japanese Patent No. 3875247, a lens having a circular shape in a plan view is disposed on a light emitting diode as a chip to control the directivity of the chip. The light exit surface of this lens, through which light exits the lens, has a shape such that a portion in the vicinity of the optical axis is a concave and a portion surrounding the concave is a convex extending continuously from the concave.

On the other hand, JP 2008-305923 A has proposed a lens that is designed to provide a more uniform surface light source. In this lens, light that has been Fresnel reflected at the light exit surface of the lens back to the light entrance surface side thereof is reflected again by total reflection to be guided toward the surface to be irradiated.

A light emitting diode as a chip emits light mostly in the front direction of the light emitting diode chip. In the lens disclosed in Japanese Patent No. 3875247, light that has been emitted in the front direction of the chip is refracted at the concave surface in the vicinity of the optical axis and diffused. As a result, the surface to be irradiated is illuminated to have a wide illuminance distribution with a reduced illuminance in the vicinity of the optical axis.

In the lens disclosed in Japanese Patent No. 3875247, however, the light emitted from the light source needs to be refracted, and therefore the difference in height between the concave and the convex must be reduced to a certain level. That is, there is a limit to a widening of the range of transmission directions for light from the light source. The lens disclosed in JP 2008-305923 A has the same limit because it is designed to distribute the light emitted from the chip by utilizing the refraction of the light.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an illuminating lens capable of further widening the range of transmission directions for light from a light source, and to provide a lighting device, a surface light source, and a liquid-crystal display apparatus each including this illuminating lens.

In order to achieve the above object, the present inventors have considered it important, in obtaining a wider range of transmission directions for light from a light source, to distribute radially the intense light that has been emitted in the front direction of the light emitting diode chip, and come up with an idea of distributing radially the light emitted in the front direction of the light emitting diode chip by utilizing intentionally the total reflection of the light. Accordingly, the present inventors have conceived an illuminating lens described below.

That is, the illuminating lens is a lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light, and includes: a light entrance surface through which the light emitted from the light source enters the lens; and a light exit surface through which the light that has entered the lens exits the lens. The light exit surface has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extends outwardly from a periphery of the first light exit surface to form a convex. The first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region. When the position of the light source on the optical axis is defined as a starting point, the transmissive region transmits light that has been emitted from the starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, and the total reflection region totally reflects light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface. The second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface.

In the illuminating lens configured as described above, the range of transmission directions for light from the light source can be widened more by utilizing positively the total reflection of light. As shown in FIG. 13, in this illuminating lens, the light is totally reflected at the total reflection region of the first light exit surface in the light exit surface 112. Then, a part of the light again is totally reflected repeatedly at the second light exit surface extending outwardly from the first light exit surface, and returns to the light entrance surface 111 side. The light that has returned to the light entrance surface 111 side passes through the light entrance surface 111, and then is reflected at the member 130 (for example, a substrate) that faces the light entrance surface 111 so as to be guided toward the surface to be irradiated. In this case, the light that has been reflected at the member 130 to be guided to the surface to be irradiated travels in the direction away from the optical axis or travels in the direction toward the optical axis, as shown in FIG. 13. In order to obtain a wider illuminance distribution on the surface to be irradiated, it is effective to control the light that has returned to the light entrance surface 111 side so as to guide the light to a specified position on the surface to be irradiated. The present invention has been made in view of the above circumstances.

The present invention provides an illuminating lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light. The lens includes: a light entrance surface through which the light emitted from the light source enters the lens; a light exit surface through which the light that has entered the lens exits the lens; and a reversing surface extending continuously from the light exit surface and leading to a periphery of the light entrance surface while curving inwardly from a periphery of the light exit surface. In this illuminating lens, the light exit surface has a first light exit surface and a second light exit surface. The first light exit surface is recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extends outwardly from a periphery of the first light exit surface to form a convex. The first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region. The transmissive region transmits light that has been emitted from a starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, when a position of the light source on the optical axis is defined as the starting point. The total reflection region totally reflects light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface. The second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface, and of totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region and then reached the second light exit surface. The reversing surface has a shape such that the light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the reversing surface is guided to the first light exit surface by total reflection.

Herein, “approximately the entire amount” means at least 90% of the entire amount. It may be the entire amount, and may be an amount slightly smaller than the entire amount.

The present invention also provides a lighting device including: a light emitting diode for emitting light; and an illuminating lens for spreading light emitted from the light emitting diode so that a surface to be irradiated is irradiated with the spread light. This illuminating lens is the above-mentioned illuminating lens.

The present invention further provides a surface light source including: a plurality of lighting devices arranged in a plane; and a diffusing plate disposed to cover the plurality of lighting devices, and configured to receive on one surface thereof light emitted from the plurality of lighting devices and to emit the light from the other surface thereof in a diffused manner. Each of the plurality of lighting devices is the above-mentioned lighting device.

The present invention still further provides a liquid-crystal display apparatus including: a liquid-crystal panel; and the above-mentioned surface light source disposed behind the liquid-crystal panel.

According to the present invention, it is possible to obtain a wider range of transmission directions for light from the light source. Furthermore, according to the present invention, the reversing surface allows the light that has returned to the light entrance surface side to be guided to a specified position on the surface to be irradiated, and thus a wider illuminance distribution on the surface to be irradiated can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illuminating lens according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the main portions of FIG. 1.

FIG. 3 is a diagram showing optical paths of light rays that reach a first light exit surface of the illuminating lens according to the first embodiment of the present invention.

FIG. 4 is a diagram showing optical paths of light rays that reach a second light exit surface directly from a light entrance surface of the illuminating lens according to the first embodiment of the present invention.

FIG. 5 is a diagram showing optical paths of light rays that are totally reflected at a total reflection region of the first light exit surface and then reach the second light exit surface of the illuminating lens according to the first embodiment of the present invention.

FIG. 6 is a diagram showing optical paths of light rays that are totally reflected at the second light exit surface and then reach the reversing surface of the illuminating lens according to the first embodiment of the present invention.

FIG. 7 is a diagram showing optical paths of light rays that are totally reflected at the reversing surface and then reach the first light exit surface of the illuminating lens according to the first embodiment of the present invention.

FIG. 8 is a schematic diagram of a lighting device according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram of a surface light source according to a third embodiment of the present invention.

FIG. 10 is a partial cross-sectional view of the surface light source according to the third embodiment of the present invention.

FIG. 11 is a schematic diagram of a liquid-crystal display apparatus according to a fourth embodiment of the present invention.

FIG. 12A and FIG. 12B are each a plan view of an illuminating lens of another embodiment.

FIG. 13 is a schematic diagram of an illuminating lens that has been conceived before.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

An illuminating lens according to the first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an illuminating lens 1 according to the first embodiment. The illuminating lens 1, which is disposed between a light source 20 having directivity and a surface to be irradiated 3, spreads light emitted from the light source 20 and emits the spread light to the surface to be irradiated 3. That is, the illuminating lens 1 widens the range of transmission directions for light from the light source. In the illuminance distribution on the surface to be irradiated 3, the illuminance is greatest on the optical axis A that is the design center line of the illuminating lens 1 and decreases almost monotonically toward the edge. The light source 20 and the illuminating lens 1 are disposed so that their optical axes coincide with each other.

Specifically, the illuminating lens 1 has a light entrance surface 11 through which the light emitted from the light source 20 enters the lens and a light exit surface 12 through which the light that has entered the lens exits the lens. The light entrance surface 11 is designed to be sufficiently smaller in size than the light exit surface 12 when viewed in the optical axis direction in which the optical axis A extends. The illuminating lens 1 has a reversing surface 15 extending continuously from the light exit surface 12. The reversing surface 15 leads to the periphery of the light entrance surface 11 while curving inwardly from the periphery of the light exit surface 12, that is, while inclining its normal direction so as to approach the light entrance surface 11 gradually.

In the present embodiment, the light exit surface 12 is axisymmetric with respect to the optical axis A. In the present embodiment, the light entrance surface 11 also is axisymmetric with respect to the optical axis A. That is, the central region 11 a and the annular region 11 b surrounding the central region 11 a of the light entrance surface 11 are in the same plane. The central region 11 a of the light entrance surface 11 is connected optically to the light source 20. It should be noted that the light entrance surface 11 need not be axisymmetric with respect to the optical axis A. For example, the central region 11 a may be recessed in a shape conforming to the shape of the light source 20 (for example, a rectangular shape) so that the light source 20 is fitted in the recess. The central region 11 a need not necessarily be joined directly to the light source 20. For example, the central region 11 a may be recessed in a hemispherical shape so that an air space is formed between the central region 11 a and the light source 20.

The light emitted from the light source 20 enters the illuminating lens 1 through the light entrance surface 11, exits the lens 1 through the light exit surface 12, and then reaches the surface to be irradiated 3. The light emitted from the light source 20 is spread by the action of the light exit surface 12, and reaches a large area of the surface to be irradiated 3.

As the light source 20, for example, a light emitting diode can be used. Light emitting diodes usually are chips with a rectangular plate shape. Therefore, it is preferable that the light entrance surface 11 of the illuminating lens 1 have a shape conforming to the shape of a light emitting diode to fit in close contact with the light emitting diode. The light emitting diode is in contact with the light entrance surface 11 of the illuminating lens 1 via a bonding agent, and connected optically to the light entrance surface 11. The light emitting diode usually is covered with a sealing resin to avoid contact with air. As a conventional sealing resin for a light emitting diode, an epoxy resin, silicone rubber, or the like is used.

The illuminating lens 1 is made of a transparent material having a specified refractive index. The refractive index of the transparent material is, for example, about 1.4 to 1.5. Examples of such a transparent material include resins such as epoxy resin, silicone resin, acrylic resin, and polycarbonate, and rubbers such as silicone rubber. Particularly, it is preferable to use epoxy resin, silicone rubber, or the like that has been used as a sealing resin for a light emitting diode.

The light exit surface 12 includes a first light exit surface 121 that is recessed toward a point on the optical axis A, and a second light exit surface 122 extending radially outwardly from the periphery of the first light exit surface 121 to form a convex. Light enters the illuminating lens 1 through the light entrance surface 11 at a wide range of angles. Light that has entered the lens at a small angle with respect to the optical axis A reaches the first light exit surface 121, and light that has entered the lens at a larger angle with respect to the optical axis A reaches the second light exit surface 122.

Next, the shapes of the first light exit surface 121 and the second light exit surface 122 will be described. For that purpose, a starting point Q (see FIG. 2) is defined first, and then light emitted from the starting point Q is assumed. As stated herein, the starting point Q is the position of the light source on the optical axis A. In the case where a light emitting diode is used as a light source, the starting point Q is the point of intersection of the optical axis A and the light emitting surface that is the front surface of the light emitting diode. That is, the starting point Q is spaced from the light entrance surface 11 by the thickness of the above-mentioned bonding agent. When an angle between the optical axis A and a line connecting the starting point Q and the boundary between the first light exit surface 121 and the second light exit surface 122 is θb, light that has been emitted from the starting point Q at an angle reaches the first light exit surface 121 or the second light exit surface 122 based on the angle θb as a threshold angle.

As shown in FIG. 2, the first light exit surface 121 includes a transmissive region 123 located in the center of the first light exit surface 121 and a total reflection region 124 located around the transmissive region 123. The transmissive region 123 transmits light that has been emitted from the starting point Q at a relatively small angle of less than a specified value of θp with respect to the optical axis A and reached the first light exit surface 121, and the total reflection region 124 totally reflects light that has been emitted from the starting point Q at a relatively large angle of θp or more with respect to the optical axis A and reached the first light exit surface 121. That is, θp is an angle between the optical axis A and a line connecting a point P and the starting point Q, when the point P is a point on the boundary between the transparent region 123 and the total reflection region 124. On the other hand, the second light exit surface 122 has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point Q and reached the second light exit surface 122, and totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region 124 and reached the second light exit surface 122 (see FIG. 4 and FIG. 5). The angle between the optical axis A and the light emitted from the starting point Q increases toward the outer edge of the second light exit surface 122. The angle of the light emitted from the starting point Q with respect to a normal line at the point on the second light exit surface 122 reached by the emitted light is the incident angle of the light with respect to the second light exit surface 122. An excessively large incident angle causes total reflection. The incident angle needs to be kept small in order to prevent total reflection. Accordingly, the second light exit surface 122 has a shape such that the angle between the normal line and the optical axis A increases with increasing distance from the optical axis A. That is, the shape of the second light exit surface 122 is a convex.

The entire second light exit surface 122 need not necessarily transmit the light emitted from the starting point Q (i.e., the second light exit surface 122 need not transmit the entire amount of the light). The second light exit surface 122 may have a shape capable of totally reflecting a part of the light emitted from the starting point Q and transmitting the remaining part of the light.

The reversing surface 15 is axisymmetric with respect to the optical axis A. In the present embodiment, the inner periphery of the reversing surface 15 is located closer to the light exit surface 12 than the periphery of the light entrance surface 11, and the inner periphery of the reversing surface 15 and the periphery of the light entrance surface 11 are connected to each other via a tubular surface 16.

The reversing surface 15 has a shape such that the light that has been emitted from the light source 20, totally reflected repeatedly at the light exit surface 12, and then reached the reversing surface 15 is guided to the first light exit surface 121 by total reflection. Then, the light that has been guided to the first light exit surface 121 by the reversing surface 15 passes through the first light exit surface 121, and thus the surface to be irradiated 3 is illuminated with the light (see FIG. 7).

It is preferable that a portion between an intermediate point of the second light exit surface 122 and the inner periphery of the reversing surface 15 is in the shape of an arc with an approximately constant radius in a cross-sectional view including the optical axis A. In the illuminating lens having such a shape, the amount of light leaking from the lens through the outer peripheral portion of the second light exit surface 122 and the reversing surface 15 (that is, the amount of light passing through the outer peripheral portion of the second light exit surface 122 and the reversing surface 15) can be reduced, and therefore the light that has returned to the light entrance surface 11 side can be utilized effectively.

Next, with reference to FIGS. 3 to 8, how the light emitted from the light source 20 travels will be described in more detail by taking the light emitted from the starting point Q as a typical example.

FIG. 3 shows optical paths of light rays that enter the lens through the light entrance surface 11 and reach the first light exit surface 121. The light ray that has reached the transmissive region 123 due to a small angle with respect to the optical axis A (see FIG. 2) is refracted at the first light exit surface 121 and then reaches the surface to be irradiated 3. The light rays that have reached the total reflection region 124 due to larger angles with respect to the optical axis A (see FIG. 2) are totally reflected at the first light exit surface 121 and then travel inside the illuminating lens 1.

FIG. 4 shows optical paths of light rays that enter the lens through the light entrance surface 11 and reach the second light exit surface 122. The light rays that have reached the second light exit surface 122 are refracted at the second light exit surface 122 and then reach the surface to be irradiated 3.

FIG. 5 shows optical paths of light rays that are totally reflected at the total reflection region 124 of the first light exit surface 121 as described in FIG. 3 and reach the second light exit surface 122. The light rays that have reached the second light exit surface 122 are totally reflected one or more times at the second light exit surface 122 so that they travel along the second light exit surface 122 in the illuminating lens 1. Although not illustrated here, some of the light rays are not totally reflected at the second light exit surface 122 and exit the illuminating lens 1.

FIG. 6 shows optical paths of light rays that are totally reflected at the second light exit surface 122 as described in FIG. 5 and reach the reversing surface 15. The light rays that have reached the reversing surface 15 are totally reflected one or more times at the reversing surface 15 so that they travel toward the first light exit surface 121. Although not illustrated here, some of the light rays are not totally reflected at the reversing surface 15 and exit the illuminating lens 1.

FIG. 7 shows optical paths of light rays that are totally reflected at the reversing surface 15 as described in FIG. 6 and again reach the first light exit surface 121. Since the light rays that have again reached the first light exit surface 121 are now incident on the first light exit surface 121 at a smaller angle, they are refracted at the first light exit surface 121 and reach the surface to be irradiated 3.

In the illuminating lens 1 configured as described above, the most part of the light that has been emitted from the light source 20 and reached the transmissive region 123 located in the center of the first light exit surface 121 is refracted at the transmissive region 123, and thus the area surrounding the optical axis A of the lens on the surface to be irradiated 3 is irradiated with the refracted light. On the other hand, the most part of the light that has been emitted from the light source 20 and reached the total reflection region 124 located on the peripheral side of the first light exit surface 121 is totally reflected at the total reflection region 124. The most part of the totally reflected light exits the lens through the first light exit surface by the action of the second light exit surface 122 and the reversing surface 15, and then the surface to be irradiated 3 is irradiated with that light. Furthermore, the most part of the light that has been emitted from the light source 20 and reached the second light exit surface 122 is refracted at the second light exit surface 122, and thus the area away from the optical axis A of the lens on the surface to be irradiated 3 is irradiated with the refracted light. Accordingly, the illuminating lens 1 of the present embodiment allows the range of transmission directions for light from the light source 20 to be widened further.

Furthermore, in the present embodiment, the light that has returned to the light entrance surface 11 side also can be guided to a specified position on the surface to be irradiated 3 by the reversing surface 15. As a result, a wider illuminance distribution on the surface to be irradiated 3 can be obtained. In addition, such control of the light that has returned to the light entrance surface 11 side makes it possible to prevent the illuminance distribution on the surface to be irradiated 3 from being influenced by the configuration and reflectance of a structural member disposed behind the illuminating lens 1.

The illuminating lens of the present invention also is applicable to light sources (such as lasers and organic ELs) as well as light emitting diodes.

In the present embodiment, the light exit surface 12 is axisymmetric with respect to the optical axis A (circular shape in plan view). The light exit surface 12, however, need not be axisymmetric with respect to the optical axis A. For example, as shown in FIG. 12A, the light exit surface 12 may have an elliptical shape when viewed from the optical axis direction. This illuminating lens 1 is suitable particularly for an elongated light source 20. Alternatively, as shown in FIG. 12B, the light exit surface 12 may have a rounded rectangular shape when viewed from the optical axis direction.

Second Embodiment

FIG. 8 is a schematic diagram of a lighting device 7 according to a second embodiment of the present invention. This lighting device 7 includes a light emitting diode 2 for emitting light, and an illuminating lens 1 of the first embodiment for spreading light emitted from the light emitting diode 2 so that the surface to be irradiated 3 is irradiated with the spread light.

The light emitting diode 2 is in contact with the light entrance surface 11 of the illuminating lens 1 via a bonding agent, and connected optically to the light entrance surface 11. The light that has exited the illuminating lens 1 through the light exit surface 12 reaches the surface to be irradiated 3, and thus the surface to be irradiated 3 is illuminated with that light.

Light generation in the light emitting diode 2 has no directivity in itself, and a light emitting region has a refractive index of at least 2.0. When light from the light emitting region enters a low refractive region, the refraction of the light at the interface causes the light to have the maximum intensity in the normal direction of the interface and to have a lower intensity as the angle of the light with respect to the normal line increases. As described above, since the light emitting diode 2 has high directivity, it is necessary to widen the range of transmission directions for light therefrom using the illuminating lens 1 to illuminate a larger area.

Third Embodiment

FIG. 9 is a schematic diagram of a surface light source 9 according to a third embodiment of the present invention. This surface light source 9 includes a plurality of lighting devices 7 of the second embodiment arranged in a plane, and a diffusing plate 4 disposed to cover the plurality of lighting devices 7. The lighting devices 7 may be arranged in a matrix as shown in FIG. 9. They may be arranged in a staggered manner.

The surface light source 9 includes a substrate 8 facing the diffusing plate 4 with the lighting devices 7 being disposed therebetween. As shown in FIG. 10, the light emitting diode 2 of each lighting device 7 is mounted on the substrate 8. In the present embodiment, a reflecting plate 6 is disposed on the substrate 8 to cover the substrate 8 with the light emitting diodes 2 being exposed.

The lighting device 7 emits light to one surface 4 a of the diffusing plate 4. That is, the one surface 4 a of the diffusing plate 4 is the surface to be irradiated 3 that has been described in the first and second embodiments. The diffusing plate 4 emits the light received on its one surface 4 a from the other surface 4 b in a diffused manner. The lighting devices 7 emit light individually toward a large area of the one surface 4 a of the diffusing plate 4 so that the one surface 4 a has a uniform illuminance, and upon receiving this light, the diffusing plate 4 emits the light diffusely. As a result, the surface light source capable of emitting light having less uneven brightness in the plane is obtained.

The light emitted from the lighting device 7 is diffused by the diffusing plate 4 so that the diffuse light returns to the lighting device side or passes through the diffusing plate 4. The light that has returned to the lighting device side and struck the reflecting plate 6 is reflected at the reflecting plate 6 and again enters the diffusing plate 4.

Fourth Embodiment

FIG. 11 is a schematic diagram of a liquid-crystal display apparatus according to a fourth embodiment of the present invention. This liquid-crystal display apparatus includes a liquid-crystal panel 5, and a surface light source 9 of the third embodiment disposed behind the liquid-crystal panel 5.

A plurality of lighting devices 7 each including the light emitting diode 2 and the illuminating lens 1 are arranged in a plane, and the diffusing plate 4 is illuminated by these lighting devices 7. The underside (one surface) of the diffusing plate 4 is irradiated with the light emitted from the lighting devices 7 to have a uniform illuminance, and then the light is diffused by the diffusing plate 4. Thus, the liquid-crystal panel 5 is illuminated by the diffused light.

It is preferable that an optical sheet such as a diffusing sheet or a prism sheet is disposed between the liquid-crystal panel 5 and the surface light source 9. In this case, the light that has passed through the diffusing plate 4 further is diffused by the optical sheet and illuminates the liquid-crystal panel 5.

The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this specification are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein. 

What is claimed is:
 1. An illuminating lens for spreading light emitted from a light source so that a surface to be irradiated is irradiated with the spread light, the lens comprising: a light entrance surface through which the light emitted from the light source enters the lens; a light exit surface through which the light that has entered the lens exits the lens; and a reversing surface extending continuously from the light exit surface leading to a periphery of the light entrance surface while curving inwardly from a periphery of the light exit surface, wherein the light exit surface has a first light exit surface and a second light exit surface, the first light exit surface being recessed toward a point on an optical axis of the illuminating lens, and the second light exit surface extending outwardly from a periphery of the first light exit surface to form a convex, the first light exit surface has a transmissive region located in the center of the first light exit surface and a total reflection region located around the transmissive region, the transmissive region being capable of transmitting light that has been emitted from a starting point at a relatively small angle with respect to the optical axis and then reached the first light exit surface, when a position of the light source on the optical axis is defined as the starting point, and the total reflection region being capable of totally reflecting light that has been emitted from the starting point at a relatively large angle with respect to the optical axis and then reached the first light exit surface, the second light exit surface has a shape capable of transmitting approximately the entire amount of light that has been emitted from the starting point and then reached the second light exit surface, and of totally reflecting approximately the entire amount of the light that has been totally reflected at the total reflection region and then reached the second light exit surface, and the reversing surface has a shape such that the light that has been emitted from the light source, totally reflected repeatedly at the light exit surface, and then reached the reversing surface is guided to the first light exit surface by total reflection.
 2. The illuminating lens according to claim 1, wherein the light exit surface is axisymmetric with respect to the optical axis.
 3. The illuminating lens according to claim 1, wherein an inner periphery of the reversing surface is located closer to the light exit surface than the periphery of the light entrance surface, and the inner periphery of the reversing surface and the periphery of the light entrance surface are connected to each other via a tubular surface.
 4. The illuminating lens according to claim 1, wherein a portion between an intermediate point of the second light exit surface and an inner periphery of the reversing surface is in the shape of an arc with an approximately constant radius in a cross-sectional view including the optical axis.
 5. The illuminating lens according to claim 1, wherein the entire second light exit surface transmits the light that has been emitted from the starting point.
 6. The illuminating lens according to claim 1, wherein the second light exit surface totally reflects a part of the light that has been emitted from the starting point and transmits the remaining part of the light.
 7. A lighting device comprising: a light emitting diode for emitting light; and an illuminating lens for spreading light emitted from the light emitting diode so that a surface to be irradiated is irradiated with the spread light, wherein the illuminating lens is the illuminating lens according to claim
 1. 8. A surface light source comprising: a plurality of lighting devices arranged in a plane; and a diffusing plate disposed to cover the plurality of lighting devices, the diffusing plate being configured to receive on one surface thereof light emitted from the plurality of lighting devices and to emit the light from the other surface thereof in a diffused manner, wherein each of the plurality of lighting devices is the lighting device according to claim
 7. 9. The surface light source according to claim 8, further comprising: a substrate on which the light emitting diode included in each of the plurality of lighting devices is mounted, the substrate facing the diffusing plate with the plurality of lighting devices being disposed therebetween; and a reflecting plate disposed on the substrate to cover the substrate with the light emitting diodes being exposed.
 10. A liquid-crystal display apparatus comprising: a liquid-crystal panel; and the surface light source according to claim 8 disposed behind the liquid-crystal panel. 